Contact lenses have been used commercially to improve vision since the 1950s. The first contact lenses were made of hard materials. Although these lenses are still currently used, they are not suitable for all patients due to their poor initial comfort and their relatively low permeability to oxygen. Later developments in the field gave rise to soft contact lenses, based upon hydrogels, which are extremely popular today. Many users find soft lenses are more comfortable, and increased comfort levels can allow soft contact lens users to wear their lenses longer than users of hard contact lenses.
Silicone hydrogel materials have proven to be very successful contact lens materials. They are typically formed by copolymerizing a mixture of silicone-containing monomers or macromers with hydrophilic monomers. The amount of water absorbed by the final hydrated material can be controlled by selecting the type and amount of hydrophilic monomer or monomers. Some silicone hydrogels have wettable surfaces, and others have surfaces with poor wettability, even when the water content of the hydrated material is relatively high.
If the surface of a silicone hydrogel material has poor wettability, then surface treatment is typically required in order to make it suitable for use in a contact lens. Silicone hydrogels that are wettable with or without surface treatment, such as those disclosed in U.S. Pat. No. 7,052,131, can have substantial quantities of silicon on their surfaces. It may be that the surfaces of even such wettable lenses may be made more biocompatible if they contained reduced amounts of silicon. See, e.g., U.S. Patent Application 2012/0026458, paragraph [0005] and PCT Patent Application WO2008/005752 Example 4.
It has now been surprisingly found that the silicon on the surface of silicone-containing lens can be substantially reduced with exposure to fluoride ions, while the bulk properties of these lenses can be left largely or completely unchanged.